1. Field of the Invention
This invention relates generally to guidewires and, more specifically, to urological guidewires adapted for insertion and instrument guidance through the urological conduit.
2. Discussion of Related Art
The first step in a typical endoscopic urological procedure is placement of a guidewire into the patient""s urological system. When operatively disposed, the guidewire typically extends from outside the patient, through the urethra, the bladder, the ureter, and into the kidney. The guidewire allows a variety of specialized tools, such as catheters and endoscopes, to be repeatedly positioned in the urological system with ease, safety, and efficiency.
Urological guidewires of the past have typically been provided with properties relating to flexibility, lubricity, and stiffness. Each guidewire has tended to emphasize one of these properties along its entire length, in order to provide certain advantages at different points in the procedure. For example, due to the serpentine configuration of a ureter, the initial or xe2x80x9caccessxe2x80x9d guidewire is required to have a high degree of flexibility to facilitate easy insertion. However, once the flexible access guidewire is in place, it is ill-suited for the placement of instruments. By comparison, stiffer guidewires facilitate the insertion of instruments, because they tend to straighten out the anatomy in a way that flexible guidewires cannot. By straightening the anatomy and providing a more rigid guide element, instruments can be more easily inserted over the guidewire to reach an operative site.
In the past, before instrumentation could be inserted into the patient, the flexible access guidewire had to be exchanged for a stiffer, xe2x80x9cworkingxe2x80x9d guidewire. This was accomplished by placing an exchange sheath (a small-diameter flexible tube) over the access guidewire and then removing the access guidewire, leaving the sheath in place in the urological system. After the access guidewire was removed from the sheath, the stiffer, working guidewire was then inserted into the exchange sheath and the sheath removed. This left the working guidewire in place of the previous access guidewire. Unfortunately, this four-step procedure was required every time one guidewire was exchanged for another guidewire.
In some cases, the flexible access guidewire was incapable of being fully inserted, typically due to some obstruction such as a urological stone or stricture in the urological system. Under these circumstances, it became desirable to substitute a xe2x80x9cslipperyxe2x80x9d guidewire for the access guidewire. The slippery guidewire provided a high degree of lubricity, typically due to a specialized hydrophilic coating, which facilitated placement past the obstruction. Again, the four-step exchange procedure was required to insert the slippery guidewire. In some cases, the four-step procedure was required to replace the slippery guidewire, perhaps with the access guidewire, in order to achieve the ultimate, desired position within the urological system. Finally, the four-step replacement procedure would then be required once more to replace the access guidewire with the working guidewire.
Alternatively, in those cases where the slippery guidewire was able to achieve the ultimate, desired position in the urological system, it also presented disadvantages for the placement of instrumentation. Slippery guidewires tend to be so lubricious that they can actually fall out of the urological system, purely due to gravitational forces. Under these circumstances, the entire guidewire-placement procedure must be restarted. Accordingly, even with a slippery guidewire in place, it required the four-step, replacement procedure to substitute the working guidewire before the placement of instrumentation could begin. It can be appreciated that in some cases a minimum of three guidewires were needed, along with multiple applications of the four-step procedure for the exchange of the guidewires.
A common method of joining two metals is welding, soldering, or bonding via an adhesive. In the case of a urological guidewire, a metal mandrel, or core, is often joined to a coaxially-oriented metal coil by these methods. These processes are very operator dependent, and if not properly accomplished, can result in separation of the joined components within the patient.
The present invention overcomes these deficiencies of the prior art and provides a guidewire with a highly flexible, kink-resistant tip providing easy access. This tip can be coated with a lubricious, hydrophilic compound which facilitates passing the guidewire beyond stones and obstructions. A central area of the guidewire features a stiff construction which facilitates the passage of instruments over the guidewire. A proximal portion is provided with moderate flexibility which facilitates the retrograde threading of the guidewire into the guidewire channel of an instrument.
The distal floppy tip of the guidewire consists of a kink-resistant tapered Nitinol core which is covered with a small-diameter stainless steel coil. A method for attaching these two dissimilar metals is achieved with a mechanical locking feature. This mechanical lock is stronger than welding, soldering, braising, or gluing. Nevertheless, a small amount of solder or adhesive can be used to cover and encapsulate the mechanical lock. This process reduces the dependency on a welded or glued joint by replacing the joint with a mechanical interlock. The interlock can still be encapsulated by weld, solder, or adhesive, but the majority of the strength of the joint is now provided by the two parent materials. This method is particularly useful in cases where the components to be joined are made of dissimilar metals. The strength of the resulting joint is of significant advantage to the guidewire and greatly increases the safety of the procedure.
In a preferred embodiment, the urological guidewire has three regions of specific flexibility. The distal region includes a floppy distal tip with a very low coefficient of friction making it relatively slippery. A central section of the guidewire is relatively non-slippery, thereby facilitating the passage of instrumentation, while a proximal section is provided with a medium degree of lubricity. Materials such as Nitinol stainless steel, platinum, gold, and silver can be used in the various sections. A mechanical lock forged between dissimilar metals can be encapsulated in urethane, solder, adhesive, or by insert-molding a polymer.
In one aspect, the invention includes a urological guidewire having a distal section with a first flexibility, a first lubricity, and a first length. A central section is also provided, which has a second flexibility, a second lubricity, and a second length. On the side of the central section opposite the distal section, a proximal section has a third flexibility, a third lubricity, and a third length. The third flexibility is greater than the second flexibility, but less than the first flexibility. The second lubricity and the third lubricity are less than the first lubricity. Finally, the first length is greater than the third length and less than the second length.
In another aspect of the invention, the urological guidewire includes a core formed of the first metallic material and extending toward an end of the guidewire. A coil including a plurality of convolutions extends around the core at the end of the guidewire and is formed of a second metallic material different than the first metallic material. A mechanical interlock is formed between the coil and the core to inhibit separation of the coil from the core. This mechanical interlock can include an enlargement having a lateral dimension greater than the diameter of the core at the distal end of the core. A bonding material encapsulates the enlargement and bonds the enlargement to the coil.
The mechanical interlock can also be formed by providing the coil with a penultimate convolution having a first radius, and an ultimate convolution having a second radius less than the first radius to form a bridge. Portions of the core can be bent over or around the bridge to form the mechanical interlock.
In an associated method of manufacture, the enlargement of the core can be mechanically bonded to the coil. Alternatively, the coil can be provided with the bridge and the core can be bent over or around the bridge and fixed to itself to form a mechanical interlock. These and other features and advantages of the invention will be more apparent with a discussion of preferred embodiments and reference to the associated drawings.